This invention is in the general field of design of structural components. More particularly, it relates to components particularly advantageous for aircraft, spacecraft and other vehicles, which must be lightweight relative to their strength and stiffness. In further particularity, it relates to improvements in the structure and geometry of corrugated sheets.
One well known technique for achieving the aforementioned stiffness and strength relative to weight in structural components which include a sheet, is to use a corrugated sheet fabricated from suitable metals or fiber reinforced resin matrix composites. Such a sheet, instead of being flat, is corrugated with the corrugations being oriented transverse to the lengthwise dimension of the sheet. The rigidity of such a corrugated sheet may be increased by providing it with secondary corrugations extending from the side walls. The local strength and bending stiffness of corrugated sheets may be further increased by bonding separate cap strips to the main corrugations wherein the cap strips support the compressive load.
Although the aforementioned technique is well known, there is a constant need for structures with improved strength to weight relationships. For corrugated sheets constructed from composite materials, problems exist in orienting the fibers so they are appropriately spaced and not bunched in some areas and too sparsely distributed in others so that all of the fibers are relatively evenly tensioned rather than being slack or strained, resulting in local weaknesses in the corrugated sheet. Use of the aforementioned technique with diffusion bonded and superplastic formed metals or composites often results in decreased strengths and rotational stiffness due to insufficient stabilization of the edges of the main corrugations. Further, corrugated structures are highly susceptible to impact damage along the exposed edges and flat surfaces of the main corrugations. In practice, these and other deficiencies result in a loss in structural efficiency which necessitates a heavier structure for a given load and span.
Accordingly, it is an object of this invention to provide a corrugated sheet structure with improved strength and stiffness relative to weight.
Further, it is an object of the present invention to provide an improved corrugated sheet design for bearing compressive loads and for use in forming the structure of aircraft and spacecraft.
Still further, it is an object of this invention to provide an improved corrugated sheet structure fabricated from metal or fiber reinforced composites. A related object is to solve the problems inherent in providing structural components with corrugated sheets made from metal or fiber reinforced composites.
Yet another object of this invention is to provide a corrugated sheet design that is capable of being fabricated as a unitary structure with repeated corrugated segments and which has the combined characteristics of ease of repair, minimum volume displacement and ease of fabrication.
Still another object is to provide a corrugated sheet that is resistant to damage from contact at exposed edges and surfaces and has improved rotational support.
These and other objects are attained by providing a strong, lightweight corrugated sheet of a particular shape. In the preferred form, the invention comprises a plurality of elongated corrugation segments in parallel side by side adjacency and extending across the sheet. Each corrugation segment is generally U-shaped in cross-section and rigidly secured to each adjacent segment to form a sheet. Each corrugation segment includes straight side walls and top and bottom crowns which are part-cylindrical and not flat as in prior art. The side walls of each corrugation segment may be corrugated to increase the strength and rigidity of the sheet. In addition, a cap strip may be bonded to each part-cylindrical crown, and the longitudinal edges of the cap strip may be crimped down over the adjacent side wall thereby forming a flange which increases the local buckling strength and damage resistance of the corrugation segment.